docs: def keys_values(self):
          """Key values might be a list or not, always return a list."""
          keys_values = []
          for value in self.keys.values():
              if isinstance(value, list):
                  keys_values += value
              elif isinstance(value, basestring) and not value.startswith('-'):
                  # Avoid -99. Should be fixed in geozones
                  keys_values.append(value)
              elif isinstance(value, int) and value >= 0:
                  # Avoid -99. Should be fixed in geozones
                  keys_values.append(str(value))
          return keys_values